Normal injection screws, steel rollers, and other kinds of rotational equipment (e.g. impellers, turbines, or pumps) are run at high pressure, high mechanical torsion, high friction, and highly corrosive conditions. As such, the surface of the screw or impeller should be treated (e.g. ion nitriding or metal spraying) to improve its endurance. The injection screw material is usually alloy steel containing aluminum, chromium, and molybdenum such as SACM645, SKD61, and the like. The injection screw may have a hardness Hv of greater than 800 after nitriding, which can be utilized as plastic plasticizer screws and plastic melting barrels of a general piping set due to its excellent abrasion resistance. However, the above material has a poor corrosion resistance. A ceramic material (e.g. TiN or CrN) can be coated on the screws or the other rotational equipment by persons with ceramic coating skills (e.g. CVD) to improve the corrosion resistance of the above material. Although the ceramic material has high hardness and corrosion resistance, the ceramic material and a metal substrate have a poor bonding strength therebetween. In addition, the ceramic material is brittle, and it easily suffers cracking and peeling after being used for a period of time.
Accordingly, a novel coating for overcoming the above problem is called for.